Cable



y 1936. J. J. MORRISON 2,049,073

CABLE Filed March 21, 1953 1920972592": JQME?) J MORE/SON,

Patented July 28, 1936 UNITED STATES aoiaoia CABLE James J. Morrison,Worcester, Mass, assignor to The American Steel and Wire Company of NewJersey, a corporation of New Jersey Application March 21, 19.?3, SerialNo. 661,982 3 Claims. (Cl. 173-266) This invention relates to electriccables, particularly when for high voltages; for example, operating at2500 volts or higher. g 1

In such high voltage cables it has become com- 5 mon practice to makeuse of a metallic shieldi over the insulation on the conductor orconductors, in order that deterioration due to corona may be reduced toa minimum; such shielding being in the form of a metallic tape, eithersolid or woven, but relatively inelastic as compared with theinsulation. With such type of shielding, any abrupt bend duringthe'process of manui'acture or during installation maycause deformationof the metal and result in voids or pockets between the shielding andthe surface of the insulation, thus increasing the possibility ofdeterioration oi the insulation at these spots. Moreover, duringoperation the cable is subject to cycles of expansion and contraction,resulting in additional loosening of the shielding on the surface of theinsulation. I Remembering that the highly conductive metals arecharacterized byinelasticity, the reasoni'or the above is obvious. Forinstance, copper g5 tape, frequently used for shielding because of itsdesirable non-magnetic. properties, has been found in practice toassume-a permanent set when distorted beyond its rather low elasticlimit. This naturally causes its separation fromthe underly- 30 inginsulation when the latter returns to a normal shape, and results in theabove undesirable conditions.

One of the objects of the present inventor is to eliminate or diminishthis characteristic of' 3:, shielded cables. This is done by providing anew and improved cable shielding. Generally speaking, this shieldingincludes a conductive material and a relatively elastic material, thelength ratio and association of these two being arranged 40 so the majorportion of any strain applied to the shielding is applied to the elasticmaterial. More specifically, it is a tape fabricated in whole or in partfrom relatively elastic strands having conductive wire helically woundthereon. Thus,

45 the stretched length of the wire will exceed that of the elasticmaterial. Any strains within the limits of cable handling and operationare taken by these elastic strands, while the wire merely coils oruncoils, under the resilient effect of the 50 former, without anypermanent distortion;

Experiments have demonstrated that a shielding of this new type, whenapplied to the surface of a conductor insulation, possesses the elasticproperties of the strand elements, and will meet 55 bending conditionsin handling as well as the operating cycles of expansion andcontraction, without being loosened or deformed, and that the shieldingprotection given by the metallic covering will be constant withconsequent increased life for the cable. 5

While the application of the shielding in the form of a tape isadvisable from the standpoint of ease of manufacture, it may be appliedin the form of a wind, braid, or the like, without sacrifice of itsvaluable properties. Such a type of 10 shielding is particularlyadaptable to conductors insulated with rubber compound, since the tapemay be applied to the surface of the rubber insulation beforevulcanization, thereby securing maximum adhesion of the shielding to thesurl5 face of the rubber insulation, during the vulcanizing process.This shielding may be saturated with a suitable impregnation possessingprotective characteristics, thus providing additional shielding againstdeterioration of the 20 insulation without detracting from the otherdesirable features produced by its use.

In the accompanying drawing, single and three-conductor constructionsareshown, but this invention is applicable to any type or constructionof cable in which shielding of the conductor insulation is desirable.

Figures 1 and 2 show the single conductor cable, Figures 3 and 4 thethree-conductor one, and Figures 5 and 6 another single conductor cableto which, the shielding is diflerentiy applied.

In Figures 1 and 2 the condufior, which may be either solidor stranded,is rlipre'sented by I; and the insulation around the conductor is shownas 2. The new shielding is represented by 3, in this case shown asapplied in the form of tape,

- although its application may be in the form of a braid, wind, or otherconvenient means. The strands are numbered 3 and the metal helicallywound thereover as 3. The strands may be of 40 cotton, and they need notnecessarily all carry wire. 4' indicates the outer protective cover,which may be in the form of a lead sheath, tape, braid, wind, armor orany required combination of such covers.

Figures 3 and 4 show a three-conductor cable, although it must beunderstood that this method of shielding may be used on any number ofconductors. In these an individual conductor, which may be either solidor stranded, is shown as 5, with its insulation 6. The new shielding isshown applied as a tape i, although its application maybe in other form,as cited above. 8 represents a binder tape over the cabled conductors,which are assembled with fillers of rubber,

tape, armor, or any required combination for insuring protection. It mayalso be desirable to place conducting strands in the interstices of anymultiple conductor construction which will be in intimate contact withthe shielding I, and provide means for any heavy flow of current toground.

Figures 5 and 6 showa further modification of the use of the new type ofshielding, in which it is applied between the conductor and the innersurface of the insulation, as well as over the outer surface of theinsulation. Here, It represents the conductor and H the inner shielding.I! shows the conductor insulation, with the outer shielding lit. Theouter protective cover or covers are indicated by H.

By the use of the elastic shielding, as shown by H, the possibility ofvoid formations between the conductor and insulation during operatingcycles of expansion and contraction, or from sharp bends in handling isdecidedly reduced with consequent reduction in the possibility ofinternal corona cutting on the insulation. While shown in the singleconductor construction, the use of the invention for an internal shieldis also applicable in multiple conductor constructions.

I claim:

1. A high-voltage electric power cable including the combination of aconductor, insulation around said conductor, and shielding arranged inintimate contact with at least one of the surfaces of said insulation,said shielding including relatively elastic strands having conductivewire wound thereon so that it is sumciently elastic to accommodatedistortion of said insulation.

2. A high-voltage electric power cable including the combination of aconductor, rubber insulation around said conductor,- and shieldingarranged to protect said rubber insulation from the electrical 'eflectscaused by high-voltage currents carried by said conductor, saidshielding being fabricated from conductive wire and an elastic materialthat are associated so that the stretched length of the former exceedsthat of the latter, and said rubber insula tion being vulcanized to saidshielding so that there are no voids between the two.

3. A high-voltage electric power cable including the combination of aconductor, rubber insulation around said conductor, and shieldingarranged to protect said rubber insulation from the electrical eii'ectscaused by high-voltage currents carried by said conductor, saidshielding including relatively elastic strands having conductive wirewound thereon so that it is sufllclentiy elastic to accommodatedistortion of said insulation, and said rubber insulation beingvulcanined to said shielding so that there are no voids between the two.

JAMES J. MORRISON.

